In situ combustion process



July 17, 1962 J. w. TOOKE IN srru COMBUSTION PROCESS Filed Oct. 2, 1958 OXYGEN 30 PRODUCTION 6g LP I AIR OR FUEL GAS PRODUCT WELL INJECTION WELL I OVERBURDEN COKE L M mo m E R IsuBsTRATuMI I TAR,O|L OR SHALE FORMATION INVENTOR.

J. W TOOKE BY 14% 0 A TTORNEIS 3,044,545 IN SITU COMBUSTION PROCESS James W. Tooke, Bartlesvillc, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 2, 1958, Ser. No. 764,994 8 Claims. (Cl. 166-11) This invention relates to a process for recovering components of a carbonaceous deposit by in situ combustion. A specific aspect of the invention pertains to the conversion of coke, left in a carbonaceous stratum by an inverse in situ combustion wave, into the fuel gas and utilizing the resulting fuel gas in effecting an inverse in situ combustion process.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move through the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and, in the case of inverse drive, upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a bore hole thereon, followed by injection of air through the ignition borehole in the stratum, constitutes a direct drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum frequently plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difficulty and to permit the continued progress of the combustion zone through the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes. Most of the techniques utilized are also applied to the gasification coal veins.

When a carbonaceous stratum is produced by inverse in situ combustion with the fire front moving thru. the stratum countercurrently to the flow of air, a substantial carbonaceous or coke residue remains in the stratum. after passage of the fire front therethru. This coke residue is 1100 to 1700" F. Tests on tar sands indicate that the coke residue amounts to about 3 weight percent of the stratum. Hence, recovery of this valuable fuel in usable form is highly desirable. This invention is concerned with the recovery of this residual coke in the form of a combustible fuel gas and utilization of the fuel gas in an inverse in situ combustion process in a carbonaceous stratum.

Accordingly, it is an object of the invention to provide an improved process for the recovery of components of a carbonaceous deposit by in situ combustion. Another object is to utilize the hot coke deposit remaining in a carbonaceous stratum, after an inverse burning wave has passed therethru, in the recovery of hydrocarbons and other valuable components in the stratum in an inverse in situ combustion process effected in a carbonaceous stratum. A further object is to provide a more efficient process for recovering hydrocarbons by in situ combustion which effects better utilization of heat. It is also an object of the invention to increase the rate of advance of an inverse in situ combustion front and also the percentage of recovery of carbonaceous material from a stratum.

States Patent Q 3,044,545 Patented July 17, 1962 "ice an inverse in situ combustion process in a carbonaceous.-

stratum. When air alone is injected into the hot residual coke, the injected air burns a portion of the residual 'hot' coke and drives another portion out as gaseous hydrocarbon and CO, both of which are utilizable as fuel gas in assisting in the movement of an inverse burning wave in a carbonaceous stratum. In practicing the invention with a mixture of air and steam the following reactions take place:

Water gas reaction-'C+H O=CO+H Producer gas reaction- 108 C+.54 O =l.08 CO If 4.32 pounds of air is injected per pound of steam enough heat is developed by burning the coke with oxygen to sustain the endothermic Water gas reaction without reduction in stratum temperature. However, it is not essential to maintain the original stratum temperature in all cases and the amount of injected air may range from about 2 to 8 pounds per pound of steam. The heating value of the produced fuel gas is about 200 Btu. per cubic foot. Since the amount of coke left in the stratum after the inverse burning wave is about 3 weight percent of the stratum, the fuel gas produced is more than sufficient to feed-an inverse in situ combustion process in the same stratum to keep ahead of the fuel gas process, itself.

The air and steam may be injected in admixture or in separate streams into the stratum thru the same or thru separate boreholes so that these gases admix in'the. stratum and pass into thehot coke. Ordinarily in field operation, a carbonaceous stratum is produced by causing a fire front to pass thru successive annular sections of stratum. defined by successive rings of wells (radial drive) or rectangular sections defined by successive straight rows of wells (line drive). The wells immediately behind the fire front in an inverse air injection process are production wells while those immediately ahead of the fire front are wells and the next ring or row of wells in the path of the combustion front become air injection wells The production of fuel gas from the hot partially burned out stratum thru which the inverse burning wave has passed is effected between rows of wells or rings of wells in a section of the hot stratum thru which the combustion front has passed and the fuel gas, or at least a portion thereof, so produced is injected along with the injected air supporting the inverse burning wave in a section of virgin stratum.

The injection of fuel gas along with the'injected air to an inverse in situ combustion process increases the rate of movement of the inverse burning front and also increases the percentage of valuable hydrocarbons recovered from the stratum during the inverse burning phase of the process. Evidence of these advantages obtained in an inverse burning process are set forth in the application of A. R. Schleicher and 'J. C. Trantharn, S, N. 767,507, filed October 16, 1958. The amount of fuel gas injected with the combustion-supporting air should be in the range of about 0.5 to 7 volume percent in order bonaceous stratum showing an arrangement of apparatus for effecting the invention. 7

Referring to the drawing, a carbonaceous stratum '10 is penetrated by wells 12, 14,16, and 18. Well 12 is a 1100 to 1700 F. While the stratum intermediate wells 16 and 18 is at such a temperature, air or other oxygen rich gas, alone, or in admixture with steam is injected thru well 18 and passes into the stratum toward well 16, effecting partial combustion of the coke (and the water gas reaction when steam is utilized). Using air alone, a substantial concentration of hydrocarbons isfound in the efiiuent fuel gas. The fuel gas thus produced is recovered thru well 16 and is passed from tubing 22 thru line 24 to air injection line 26 for injection, along with the air, thru tubing 28 into well 14. A portion of the produced fuel gas may be separately recovered thru line 30 for use in any desired manner. The gas injected thru tubing 28 into well 14 passes thru stratum to the inverse burning front which is moved toward well 14. Hydrocarbons and combustion products from combustion front .20 pass into well 12 and are recovered thru tubing 32.

Wells 12, 14, 16, and 18 each represent a well in either a ring of wells or a row of wells,-depending upon whether the process is being effected by radial drive or by line drive, respectively. When effecting the process by radial drive, well 18 is either a central well with wells 16, 14, and 12 being successively more remote rings of Wells; or well 18 represents a well in an inner ring with the other wells representing wells in outer rings of wells, generally concentric. Normally, wells 12 and 16 are in adjacent rings or rows but this is not necessarily the practice to be followed inasmuch as the hot fuel gas recovered thru tubing 22 may be injected into the stratum in any portion of the field or stratum in which an in situ combustion process is being effected. In the operation illustrated in the drawing an inverse combustion front has been passed successively from wells 18 to wells 16, then to wells 12, and the front is in the process of moving to wells 14.

While the flow of air or airadmixed with steam is shown from Well 18 to well 16, it is also feasible to inject combustion-supporting gas and/ or steam into well 16 and recover fuel gas thru well 18, in which case, line 24 must be connected with tubing 21.

When combustion front 21 arrives at or approaches well 14, injection of air and fuel gas thru an outer more remote ring of wells or line of wells (not shown) is initiated and the combustion front is moved beyond wells 14, the latter being used as production wells in the same manner as wells 12 were utilized as production wells during the movement of combustion front 20 from wells 12 to wells 14. Normally the burning out of the carbonaceous residue between wells 16 and 18 can be controlled so as to complete this. burning about the time combustion front 20 arrives at wells 14. This makes it feasible to then convert the residual hot coke in the stratum between wells 12 and 16 to fuel as while coniaoaacas bustion front 28 is being moved from wells 14 out to the next ring or row of wells. 7

It is to be understood that carbonaceous deposit" encompasses any subterranean deposit of combustible organic material including oilshale, tar sand, oil sand,

partially depleted oil sand, lignite, porous and/or fractured coal veins, and coke left by pyrolysis of the foregoing strata.

The term O -containing gas encompasses pure oxygen, air, O -enriched air, and diluted air which is capable of supporting combustion. Where the term air is used, it

is to be understood that combustion supporting O -containing gas may be used.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitationson the invention.

.1 claim:

l. A process for producing hydrocarbons from a permeable carbonaceous stratum which comprises injecting a first gas selected from the group consisting of O containing gas and a mixture of same with steam into a first section of said stratum thru which an inversely burning combustion zone has beenpassed, leaving hot coke in same at combustion supporting temperature, while said first section is at said temperature to produce fuel gas by reaction of said first gas with said coke, said gas being injected thru a first injection wellin said first section and said fuel gas being produced thru a production well therein; simultaneously maintaining a combustion zone in an unburned second section of said stratum intermediate a second production well and a second injection well therein and moving said zone thru same by feeding a mixture of combustion-supporting gas and said fuel gas in which the concentration of fuel gas is in the range of 0.5 to 7.0 volume percent to said combustion zone thru said second injection well and recovering produced hydrocarbons thru said second production well.

2. The process of claim 1 wherein the injected. gas compnses air.

3. The process of claim 1 wherein the injected gas comprises air and steam.

4. The process of claim 3 wherein the air is in the range of 2 to 8 pounds per pound of steam.

5. The process of claim 1 wherein the combustion zone is moved thru the second section from said second production well to said second injection well by igniting said second section around said production well.

6. The process of claim 5 wherein said hot fuel gas is recovered from said first section of stratum and injected into said second section of stratum while substantially at the recovery temperature.

7. The process of claim 5 wherein said mixture comprises air.

' 8. The process of claim 5 wherein said mixture comprises air and steam, said air being in the range of 2 to 8 pounds per pound of steam.

References Cited in the file of this patent UNITED STATES PATENTS 2,481,051 Uren Sept. 6, 1949 2,642,943 ,Smith et al. June 23, 1953 2,793,696 Morse May 28, 1957 2,880,803 Parker Apr. 7, 1959 

1. A PROCESS FOR PRODUCING HYDROCAARBONS FROM A PERMEABLE CARBONACEOUS STRATUM WHICH COMPRISES INJECTING A FIRST GAS SELECTED FROM HE GROUP CONSISTING OF O2-CONTAINING GAS AND MIXTURE OF SAME WITH STEAM INTO A FIRST SECTION OF SAID STRATUM THRU WHICH AN INVERSELY BURNING COMBIUSTION ZONE HAS BEEN PASSED, LEAVING HOT COKE IN SAME AT COMBUSTION SUPPORTING TEMPERATURE, WHILE SAID FIRST SECTION IS AT SAID TEMPERATURE TO PRODUCE FUEL GAS BY REACTION OF SAID FIRST GAS WITH SAID COKE, SAID GAS BEING INJECTED THRU A FIRST INJECTION WELL IN SAID FIRST SECTION AND SAID FUEL GAS BEING PRODUCED THRU A PRODUCTION 